1. Field of the Invention
Graphic recorders are known to the prior art. Typically, such recorders employ a pen or other similar recording element which is movable relative to a moving recording medium, the combined movement of the recording element and medium being controlled to produce a desired representation. The use of multiple pens for such purposes as multi-color plotting is known to the prior art.
2. Description of the Prior Art
An example of a multiple pen system is disclosed in U.S. Pat. No. 3,401,401, issued Sept. 10, 1968 to Read, et al, for Multiple Pen Cartridge, which is hereby incorporated by reference. The disclosed Read embodiment employs four pens which may be independently chosen for color selection, for example. However, the selection of each pen requires the operation of a different pen-actuating device. Thus, the movable support for the pens must also support and move an independent actuating device for each pen. The over-all mass of the moving support that results from the use of multiple pens and independent actuating elements has placed a practical limit of four pens on the Read technique.
An attempt to overcome the mass problems of multiple pen graphic recorders is disclosed in U.S. Pat. No. 4,135,245 issued Jan. 16, 1979 to Kemplin, et al for plotter with Automatic Pen-Changer, which is hereby incorporated by reference. The Kemplin system, like similar prior art systems, employs a pen repository, at which multiple pens are maintained, and a single pen recording head. The pen which is desired immediately for recording purposes is retrieved from the repository, after which the recording operation is initiated. When a pen change is desired, the recording operation stops, and the recording head returns the pen it has utilized to the repository, where it also retrieves an alternative pen, according to instructions. While this does reduce the mass of the recording pen by the mass of those pens not used, together with their associated actuating and supporting structures, it increases the recording time by the amount of time necessary to return a previously utilized pen and to retrieve the pen that it is desired to use.
Systems meeting the general description of the two systems described above are in common use. Since such systems are typically numerically controlled, each has qualities which frustrate the capabilities of the control systems. For example, heavier masses require heavier mechanisms for moving that mass, which may lead to difficulties in acceleration speed as well as precision. Greater time requirements (i.e., for pen retrieval, for example) introduce a delay not required by the control system.
An improvement over the systems described above is disclosed in U.S. patent application Ser. No. 410,504, filed on Aug. 23, 1982 by Nicholas for Graphic Recording System, which is commonly owned with the present invention, and which is hereby incorporated by reference. The Nicholas system has a multiple pen capability without the mass required for individual actuating systems for each pen. The multiple pen capability also eliminates the delays introduced by a pen retrieval operation. However, even though a single actuator is employed by Nicholas, that actuator is carried with the moving elements such that its weight must be accommodated. That actuator must be powered, requiring, in a preferred embodiment, an electrical connection with the moving elements. In addition, Nicholas discloses an embodiment which employs two positioning systems which must be controlled.